DNA (Deoxyribonucleic Acid)

What is DNA? DNA is an encoded molecule that determines traits by giving instructions to make proteins.

Discovery of DNA Structure 1953 – James Watson and Francis Crick (Nobel Prize) Rosalind Franklin

Structure of DNA Very long molecule

Structure of DNA Made of nucleotides – Each nucleotide: Sugar (deoxyribose) Phosphate group (negatively charged) Nitrogen base adenine (A) guanine (G) cytosine (C) thymine (T)

Structure of DNA Double helix – 2 strands connected like a ladder and twisted

Structure of DNA Base pairing rules – In DNA … Adenine (A) always pairs with thymine (T) Cytosine (C) always pairs with guanine (G)

Calculating % of Bases If you know % of one base, you can calculate the rest. – Example: % of adenine = 34% – Because A & T pair up, # adenine = # thymine – So, thymine = 34% – So, adenine and thymine make up 68% ( ) – So, cytosine and guanine together make up 32% (100 – 68) – Because C & G pair up, just divide 32 by 2. – So, cytosine = 16% and guanine = 16%.

Importance of Base Sequences Sequence = order of bases Sequence of bases determines the proteins made by the cell We can also use sequence to determine: – How closely 2 organisms are related – If 2 people are related (paternity) – If crime scene DNA matches suspect’s DNA